Not surprisingly, there are very few appreciable differences
between the 2-port and 4-port variations of the 5200. For the
purposes of this article, they are considered to be identical.

Where to get signals:

Most of the components do not have visible labels on the board's
silkscreen, so giving component numbers is not useful. In the
upper right corner of the area of the board that's covered by the
shielding, there is a horizontal row of components.

The Luma signal needs amplification to be useful. After probing
around on an Atari 800 (a close relative to the 5200 that
conveniently has Croma/Luma outputs built-in), I realized the
amplifier circuit they used is remarkably similar to the one
attributed to Thomas Clancy in the Classic Atari Game Systems FAQ.
Rather than try to copy the circuit on the Atari 800 or design one
from scratch, I decided to use the one given there. The only
significant difference is the addition of another level of
luminance.

In my experience, the 5200's chroma signal is sufficiently strong
that it can be used without amplification. On my own 5200, I
ran the chroma through a 2kohm resistor to "take the edge off,"
then a 1uF capacitor to filter the DC voltage off. Play around
with the resistance there to find what suits you.

To gain composite output, just tie the Luma and Chroma outputs
together into a single output.

Where to put it:

I mounted the circuits on a small project board from Radio Shack,
tapping into the appropriate points on the 5200 board with a
length of ribbon cable. I then tucked the board into the
controller storage space at the back of the console and ran the
output signals to three RCA jacks I had mounted in the removable
expansion interface cover. That way the only permanently
modified/damaged piece (the cover) is also one that is easily
replaced.